<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <style>
        .hr {
            width: 300px;
            background-color: tomato;
        }

        .hr.half-px {
            height: 1px;
            transform: scale(0.5);
        }

        .hr.one-px {
            height: 1px;
        }
    </style>
</head>

<body>
    <p>0.5px</p>
    <div class="hr half-px"></div>
    <p>1px</p>
    <div class="hr one-px"></div>
</body>

</html>